Method for constructing sea ice islands in cold regions

ABSTRACT

A method for constructing sea ice islands in cold regions in which a water impervious membrane is placed on the surface of a floating sheet of natural ice and sea water is thereafter deposited on the membrane and allowed to freeze to form an ice body having a mass such that its draft is greater than the water depth, whereby the ice island is permanently grounded. Brine is drained from the ice body through wells penetrating the upper portion of the ice body above the membrane. Alternatively, sea water can be frozen directly on the surface of the natural ice until the ice sheet is thickened sufficiently that the bottom of the ice is just above the marine floor. The ice body is cured at ambient conditions to allow brine to drain from the bottom of the body. Next, a water impervious membrane is applied to the surface of the ice body and additional sea water frozen thereon to thicken the ice body sufficiently to ground it on the marine floor and to raise the surface of the body above the surrounding floating ice. Brine is drained from the upper portion of the ice body above the impermeable membrane through wells penetrating this portion of the body.

United States Patent 1 Robinson et al.

[ 1 Nov. 26, 1974 METHOD FOR CONSTRUCTING SEA ICE ISLANDS IN CDLDREGIONS [75] Inventors: Joel P. Robinson, Los Angeles; Paul .1. Burning,La Habra, both of Calif.

[73] Assignee: Union Oil Company of California,

Los Angeles, Calif.

[22] Filed: July 23, 1973 [21] Appl. No.: 382,006

[52] US. Cl 61/46, 61/1, 61/36 A, 62/1, 62/260 [51] Int. Cl. E021)17/00, F25c 1/02 [58] Field of Search .1 61/46, 50, 1, 58, 46.5, 61/36A; 62/1, 260, 58

[56] References Cited UNITED STATES PATENTS 3,660,983 5/1972 Gill 61/13,750,412 8/1973 Fitch et a1 61/46 Primary Examiner-Jacob ShapiroAttorney, Agent, or Firm-Dean Sandford; Richard C. Hartman [57] ABSTRACTA method for constructing sea ice islands in cold regions in which awater impervious membrane is placed on the surface of a floating sheetof natural ice and sea water is thereafter deposited on the membrane andallowed to freeze to form an ice body having a mass such that its draftis greater than the water depth, whereby the ice island is permanentlygrounded. Brine is drained from the ice body through wells penetratingthe upper portion of the ice body above the membrane. Alternatively, seawater can be frozen directly on the surface of the natural ice until theice sheet is thickened sufficiently that the bottom of the ice is justabove the marine floor. The ice body is cured at ambient conditions toallow brine to drain from the bottom of the body. Next, a waterimpervious membrane is applied to the surface of the ice body andadditional sea water frozen thereon to thicken the ice body sufficientlyto ground it on the marine floor and to raise the surface of the bodyabove the surrounding floating ice. Brine is drained from the upperportion of the ice body above the impermeable membrane through wellspenetrating this portion of the body.

10 Claims, 4 Drawing Figures METHOD FOR CONSTRUCTING SEA ICE ISLANDS INCOLD REGIONS This invention relates to the construction of sea iceislands, and more particularly to a method for forming artificial seaice islands to serve as a base for operations.

Because of the increased activity in cold areas such as the polarregions, and especially in the Arctic, and the lack of land masses inmuch of the area, need exists for suitable bases from which exploratorydrilling, petroleum recovery, supply, tanker berthing and scientificoperations can be conducted. Some of these operations have beensuccessfully carried out from floating pack ice or from fast ice alongthe shore. The ice pack, which accounts for almost all of the ice coverin the Arctic ocean, is a conglomeration of very young ice and iceseveral years old. However, because of the low strength of therelatively thin, e.g., 2 to 4-foot thick sheet ice, and the vigorousforces and pressures that exist within the pack ice that tend to keep itin a continual state of fracture, the pack ice is highly unreliable asan operational site. The use of fast ice along the shore as a base foroperations is also often unsatisfactory since the desired operationalsite may not be frozen over, and often operations must be deferred untillate in the season to obtain ice of sufficient thickness to support theintended operations.

Natural ice islands, formed by a calving from a land ice mass, areoccasionally found adrift in the ice pack. Because of their substantialsize and thickness, these floating blocks are found to be excellentplatforms from which certain operations can be conducted. However, oftenthese natural ice islands can not be found at the desired location, andbecause they are usually adrift, they cannot be employed in a fixedlocation, unless the island happens to be grounded. Furthermore, evenifa natural ice island is found grounded at the desired location,experience has shown that changes in the wind, currents, or forcesexerted by surrounding pack ice can cause the ice island to break up orto be set adrift.

Attempts have been made to thicken sheets of natural sea ice by placingsea water on the surface of the ice and allowing the water to freeze. lnthis manner the sheet ice is thickened to provide additional strength.While these attempts have been somewhat successful in providing a basefor certain light operations, at least on an experimental basis, becauseof the relatively low strength and mobile nature of the sheet ice, thetechnique does not provide a suitable base for heavy duty operations ina fixed location.

Oftentimes, sea water is the only available water for ice islandconstruction. However, a major problem encountered in constructingartificial sea ice islands is that, upon freezing, the salts containedin the sea water concentrate in small pockets of highly concentratedbrine which weaken the ice. In natural, or floating sea ice, these brinepockets slowly migrate to the bottom of the ice and drain into the seawater beneath the ice. However, if the sea ice rests on the marinefloor, there is no escape for this concentrated brine, and it builds upin the bottom layers of ice, greatly weakening them. Thus, need existsfor a method for constructing artificial sea ice islands to provide'bothtemporary and permanent fixed bases from which various operations can beconducted.

Accordingly, it is a principal object of this invention to provide amethod for constructing relatively high strength, fixed location, seaice islands.

Another object of the invention is to provide a method for constructinga relatively high strength sea ice island in a fixed location from whichvarious operations can be conducted.

Still another object of the invention is to provide a method forconstructing an artificial sea ice island useful as an offshore drillingplatform.

A still further object of the invention is to provide a method forthickening natural sheet ice to provide a bottom-supported, fixedlocation, sea ice island.

Other objects and advantages of the invention will be apparent from thefollowing description and accompanying drawings, in which:

FIG. 1 is a cross-sectional view schematically illus trating a typicalsheet of natural sea ice floating on a marine body;

FIG. 2 is a cross-sectional view schematically illustrating thecompleted sea ice island;

FIG. 3 is a cross-sectional view schematically illus trating a sea iceisland during construction by an alternative method and prior tobottoming on the marine floor; and

FIG. 4 is a cross-sectional view schematically illustrating thecompleted sea ice island constructed by the alternative method.

Briefly, the invention contemplates a method for constructing sea iceislands in cold regions in which a water impervious membrane is placedon the surface of a floating sheet of natural ice and sea water isthereafter placed on the membrane and allowed to freeze 'to form an icebody having a mass such that its draft is greater than the water depth,whereby the ice island is permanently grounded. Brine is drained fromthe ice body through wells penetrating the upper portion of the ice bodyabove the membrane. Alternatively, sea water can be frozen directly onthe surface of the natural ice until the ice sheet is thickenedsufficiently that the bottom of the ice is just above the marine floor.The ice body is cured at ambient conditions to allow brine to drain fromthe bottom of the body. Next, a water impervious membrane is applied tothe surface of the ice body and additional sea water frozen thereon tothicken the ice body sufficiently to ground it on the marine floor andto raise the surface of the body above the level of the surrounding ice.Brine can be drained from the upper portion of the ice body above theimpermeable membrane through wells penetrating this portion of the body.

Artificial sea ice islands can be constructed by the method of thisinvention in any geographic region having average ambient temperaturesduring the construction period sufficiently low to freeze sea water. Asa practical matter, it is preferred that the method be practiced in aregion exhibiting average daily ambient temperatures below about 25 F.during the construction period, and most preferably below about 10 F.Average daily ambient temperatures within these ranges are encounteredin both the Arctic and Antarctic during a substantial portion of theyear.

HO. 1 illustrates a typical floating ice sheet wherein a substantiallyuniform sheet of ice 10 is floating on a marine body 12 overlying amarine floor 14. Ice sheet 10 can be part of the polar ice pack or canbe fast ice attached to the shore. Marine body 12 can be an ocean,

sea, bay, or like salt water body. Preferably, the construction site isselected at a location and construction commenced at a season of theyear during which the construction site is covered with a layer of seaice of substantially uniform thickness and having a relativelyfracture-free, smooth surface. Although the sheet of sea ice need onlyhave sufficient thickness to support the weight of the men and equipmentemployed in the construction operation, and may have an initialthickness of one foot, or less, thicker initial ice coverage ispreferred. Oftentimes, the initial ice sheet will be up to 6 feet inthickness, with coverages of 2 to 3 feet being typically encountered.

Construction of the ice island is commenced by placing water-imperviousmembrane 16 directly on the surface of the ice sheet 10 at the desiredlocation of the ice island, or at a preselected location such that driftduring the construction. operation will place the island over thedesired location at the time of grounding. This membrane can beconstructed of any material that can be applied under the ambientconditions encountered at the construction site and which remains waterimpervious at the ice temperatures encountered. Suitable materialsinclude water impervious plastic sheets, such as polyethylene, polyvinylchloride, polyurathane, elastomer, and expanded polystyrene foamsheeting; impregnated fabrics; impregnated paper such as asphaltimpregnated paper; metal foils such as aluminized paper; road oil;cutback asphalt, vinyl and the like, or a combination of thosematerials. Sea water is deposited upon water impermeable membrane 16either by flooding with sea water pumped onto the surface of themembrane, or by spraying sea water onto its surface. Either confinedflooding or free-flooding can be employed. In the confined floodingtechnique, a system of dikes having the desired shape are formed tocontain the sea water during the freezing operation. In the freeflooding technique, the sea water is placed on the surface and allowedto disperse in all directions from the point of discharge. The water isdischarged onto the membrane 16 covering the surface of the natural iceat the center of the point to be thickened, and an oval or circularpattern having its thickest portion at the middle and tapering outwardlyt the edges is usually obtained. The size and shape of the ice islandwill depend on the initial thickness of ice sheet 10, the waterdischarge rate and application technique, and the air temperature. If alarge ice island is to be formed, water can be discharged at severalpoints. The location of the discharge points relative to each other willaffect the shape of the resulting ice island. With either the confinedor free-flooding techniques, it is usually not necessary to remove snowfrom the surface ofthe ice or to otherwise prepare the surface. However,the show can be leveled to knock down the drifts, which will also packthe snowand produce better spreading of the initial floodings.

The sea water can be applied to the surface of the natural sheet icecontinuously at a rate such that freezing prevents accumulation ofexcessive depths of water or, alternatively, the ice can be floodedintermittently to a shallow depth and allowed to freeze to formsuccessive layers of ice. The depth of each layer should be about 2 to 6inches, measured at its deepest part, the optimum depth for individualflooded layers being about 4 inches. The depth of the water and theultimate thickness of each layer is thickest at the center of the body,and less towards the edges to produce the tapering thickness.

As schematically illustrated in FIG. 2, the weight of the added layersof ice 18 applied by free-flooding causes relaxation or plasticdeformation of the natural ice sheet 10 until a new point of buoyancyequilibrium is established, resulting in a buildup ofa convexo-planeshape with the convex surface laying at the interface of the originalice surface. Of course, the pattern obtained by confined flooding willbe different since the ice buildup will conform to the shape of thedike. This less tapered configuration often causes more severe stressesin the ice sheet 10 at the edge of and adjacent to the ice buildup. Theelevation of the surface of ice 18 will be somewhat higher than thesurrounding sheet ice since the larger ice mass will float higher in thewater than the thinner sheet ice.

The application of sea water to the surface of ice body 18 is continueduntil the mass of the ice body is such that its draft is greater thanthe depth of marine body 12, whereupon the ice body becomes grounded andanchored in place. As illustrated in FIG. 2, ice layers applied to thesurface subsequent to grounding can no longer cause the body to sink toa lower point of buoyancy equilibrium, thus the ice builds up above thesurface of the surrounding ice as additional layers are applied.Flooding is continued until the mass of the ice island is sufficient tosecurely anchor the island to the marine bottom, and to obtain anelevated working platform. It is preferred that additional ice layers beapplied until the surface of ice body 18 is at least about 3 feet aboveits maximum free-floating elevation to assure permanent grounding. Iceislands having surface elevations up to about 40 feet higher than thesurrounding sheet ice can be constructed, and surface elevations as muchas 10 to 30 feet above the surrounding sheet ice are readily attainable.

Brine drainage of ice 18 is accomplished by providing a series of wellsor bore holes 20 which penetrate ice 18 to a point adjacent toimpervious membrane 16. It is important that membrane 16 is notpunctured or perforated, otherwise the brine could drain into naturalice sheet 10 below impervious membrane 16. Wells 20 can be provided bypositioning a vertical conduit at the desired location of each wellprior to placement and freezing of the sea water. Upon completion of theflooding and freezing operation the conduits can be perforated toprovide drainage, or the conduits can be removed to provide the formedwell in ice 18. Also, wells 20 can be provided by drilling a series ofboreholes through ice 18 to a point immediately above imperviousmembrane 16. In either case, brine will drain from ice 18 and accumulatein wells 20, from where it can be removed by pumping. Wells 20 arespaced throughout ice mass 18 so as to provide for brine drainage fromthe ice mass, and are preferably spaced at intervals of about 20 tofeet.

In an alternative mode of practicing the invention illustrated in FIGS.3 and 4, construction of the ice island is commenced by depositing seawater directly on the surface ofice sheet 10 to form a body of ice 22.The application of water to the surface of ice body 22 is continueduntil the mass of the ice body is such that its draft approaches thewater depth of marine body 12, but is not sufficient to ground the icebody. The alternate flooding and freezing operation is then discontinuedand the ice mass cured for a sufficient period of time to allow drainageof concentrated brine from the bottom of the ice mass. The time requiredfor the brine to migrate through the ice to drain from the bottom of theice mass will depend in part upon the thickness of the ice and theambient air temperatures. However, curing of the ice prior to groundingfor a period of one to 6 months is usually adequate to obtain drainageof the concentrated brine from the ice mass.

After the ice mass has been cured, water impervious membrane 16 isplaced on the surface of ice mass 22. After impervious membrane 16 isinstalled, the application of water to the surface of the ice body isresumed to form ice body 24 until the mass of the combined ice is suchthat the draft of the ice body is greater than the water depth of marinebody 12, whereupon the ice body becomes grounded and anchored in place.As illustrated in FIG. 3, ice layers applied to the surface subsequentto grounding can no longer cause the body to sink to a lower point ofbuoyancy equilibrium, thus ice 24 builds up above the surface of thesurrounding ice as additional layers are applied. Flooding is contin ueduntil the mass of the ice island is sufficient to securely anchor theisland to the marine bottom, and to obtain an elevated working platform.The system of wells 26 is provided in the previously described manner toprovide brine drainage from ice body 24.

The method of this invention can be used to construct ice islands inwaters having depths of less than about 50 feet, and is especiallysuited for construction of ice islands in water up to about 30 feet indepth, and particularly in relatively shallow water having a depth offeet or less.

If desired, the ice island can be constructed in a plurality of layersseparated by a like plurality of water impervious membranes 16.

Also, if desired, piles or other supportive members can be frozen intothe ice during the construction process to provide an integral supportsystem for a drilling rig or other equipment to be placed upon theartificial ice island.

This invention is further illustrated by the following examples whichare illustrative of specific modes of practicing the invention and arenot intended as limiting the scope of the invention as defined by theappended claims.

EXAMPLE I This example illustrates the practice of the invention in acold region. The ice island is constructed in a marine body having adepth of about 8 feet at mean low tide. The construction site is coveredby a sheet of floating natural ice that is relatively smooth and free offractures. Snow drifts are leveled and the loose snow compacted. Thesite to be flooded is covered with polyvinyl chloride sheeting placeddirectly upon the compacted snow. The joints between adjacent sheets areoverlapped and sealed to provide a water impervious membrane. A pump isset and sea water pumped onto the surface of the ice sheet covered bythe membrane. The surface is flooded to a shallow depth of between about2 and 6 inches at its deepest portion and the water allowed to freeze.This alternate pumping and freezing operation is continued until theresulting ice body has a draft greater than the water depth so that 6pleted ice island has an elevation at its highest point about 10 feetabove the surrounding floating ice, and a contour that tapers from thecenter to the edges. A system of bore holes spaced about 30 feet apartare drilled through the ice body so as to terminate immediately abovethe membrane, and the brine that drains into the bore holes is removedby pumping.

EXAMPLE 2 This example illustrates an alternative method forconstructing sea ice islands in a cold region. The ice island isconstructed in a marine body having a depth of about 15 feet at mean lowtide. The construction site is covered by a sheet of floating naturalice that is relatively smooth and free of fractures. Snow drifts areleveled and the loose snow cover compacted. Pumps are set and sea waterpumped onto the surface of the ice sheet through a single discharge hoseto a depth of about 4 inches. Pumping is discontinued and the waterallowed to freeze. This alternate pumping an freezing operation iscontinued until the resulting ice body has a draft such that the bottomof the ice mass is about 1 foot above the marine floor at low tide. Thealternate flooding and freezing operation is discontinued and the icemass allowed to cure for a 2 month period to permit brine drainage intothe sea beneath the ice mass. Next, the surface of the formed ice massis covered with a water impervious layer of 15 pound roofing felt andcutback asphalt is applied to the roofing felt. The alternate pumpingand freezing operation is resumed and continued until the surface of theice island has an elevation at its highest point about 5 feet above thesurrounding floating ice, and a contour that tapers from the center tothe edges. A system of bore holes spaced about 25 feet apart are drilledthrough the ice body so as to terminate immediately above the membrane,and the brine that drains into the bore holes is removed by pumping.

Various embodiments and modifications of this invention have beendescribed in the foregoing description and examples, and furthermodifications will be apparent to those skilled in the art. Suchmodifications are included within the scope of this invention as definedby the following claims.

Having now described the invention, we claim:

11. A method for constructing an artificial sea ice island in a marinebody covered by a floating sheet of ice, which comprises:

placing a water impervious membrane on the surface of said floatingsheet of ice; thereafter placing sea water on said sheet of ice coveredby said water impervious membrane under ambient conditions such that thewater is frozen to form an ice body having a mass sufficiently largethat the draft of the ice body exceeds the depth of the marine bodywhereby the ice island is permanently grounded and the surface of theisland raised above that of the surrounding floating ice;

establishing a plurality of wells in the ice body above said imperviousmembrane for the drainage of brine from the ice body; and

removing accumulated brine from said wells.

2. The method defined in claim 1 wherein said sea water isintermittently placed on the surface of said sheet of ice covered bysaid water impervious membrane and allowed to freeze between placements.

3. The method defined in claim 2 wherein said sea water isintermittently placed on said ice to a depth of about 2 to 6 inches ateach placement.

4. The method defined in claim 1 wherein said sea water placed on saidsheet of ice covered by said water impervious membrane freely floodssaid surface.

5. The method defined in claim 1 wherein said marine body has a depth ofless than about 50 feet.

6. The method defined in claim 1 wherein the elevation of said iceisland is at least about 3 feet above its maximum free-floatingelevation.

7. The method defined in claim 1 wherein prior to placement of saidwater impervious membrane, sea

water is placed on the surface of said floating sheet of ice and frozento form an ice body having a mass sufficiently large that the bottom ofthe ice body is just above the marine floor, and including the step ofcuring said ice under ambient conditions for a period of time sufficientto allow brine to drain from the ice body.

8. A method for constructing an artificial sea ice island in a marinebody covered by a floating sheet of ice, which comprises:

placing a water impervious membrane on the surface of said floatingsheet of ice; placing sea water on the surface of said floating sheet ofice covered by said water impervious membrane to freely flood saidsurface to a maximum depth of about 2 to 6 inches under ambientcondition below the freezing point of said sea water; allowing the seawater placed on said ice to freeze; repeating the alternate flooding andfreezing steps to form an ice body having a mass sufficiently large thatthe draft of the ice body exceeds the depth of the marine body wherebythe ice body is permanently grounded and the elevation of the ice bodyis at least about 3 feet above its maximum freefloating elevation;establishing a plurality of wells in the ice body above said imperviousmembrane spaced about to 50 feet apart for the drainage of brine fromthe ice body; and removing accumulated brine from said wells. 9. Themethod defined in claim 8 wherein prior to placement of said waterimpervious membrane, sea water is placed on the surface of said floatingsheet of ice and frozen to form an ice body having a mass sufficientlylarge that the bottom of the ice body is just above the marine floor,and including the step of curing said ice under ambient conditions for aperiod of time sufficient to allow brine to drain from the ice body.

10. A method for constructing an artificial sea ice island in a marinebody covered by a floating sheet of ice, which comprises:

placing sea water on the surface of said floating sheet of ice to freelyflood the surface to a maximum depth of about 2 to 6 inches underambient conditions below the freezing point of water; allowing the seawater placed on said ice to freeze; repeating the alternate flooding andfreezing steps to form an ice body having a mass sufficiently large thatthe bottom of the ice body is just above the marine floor; curing theice under ambient conditions for a period of time sufficient to allowbrine to drain from the ice body; placing a water impervious membrane onthe surface of the ice body; thereafter placing additional sea water onthe surface of said ice body covered by said impervious membrane tofreely flood said surface to a depth of 2 to 6 inches under ambientconditions below the freezing point of water; allowing the sea waterplaced on said ice to freeze; repeating the alternate flooding andfreezing steps to form an ice body having a mass sufficiently large thatthe draft of the ice body exceeds the depth of the marine body wherebythe ice body is permanently grounded; continuing the alternate floodingand freezing steps until the elevation of the ice body is at least about3 feet above its maximum free-floating elevation; establishing aplurality of wells in the ice body above said impervious membrane spacedabout 20 to 50 feet apart; and

removing accumulated brine from said wells.

1. A method for constructing an artificial sea ice island in a marinebody covered by a floating sheet of ice, which comprises: placing awater impervious membrane on the surface of said floating sheet of ice;thereafter placing sea water on said sheet of ice covered by said waterimpervious membrane under ambient conditions such that the water isfrozen to form an ice body having a mass sufficiently large that thedraft of the ice body exceeds the depth of the marine body whereby theice island is permanently grounded and the surface of the island raisedabove that of the surrounding floating ice; establishing a plurality ofwells in the ice body above said impervious membrane for the drainage ofbrine from the ice body; and removing accumulated brine from said wells.2. The method defined in claim 1 wherein said sea water isintermittently placed on the surface of said sheet of ice covered bysaid water impervious membrane and allowed to freeze between placements.3. The method defined in claim 2 wherein said sea water isintermittently placed on said ice to a depth of about 2 to 6 inches ateach placement.
 4. The method defined in claim 1 wherein said sea waterplaced on said sheet of ice covered by said water impervious membranefreely floods said surface.
 5. The method defined in claim 1 whereinsaid marine body has a depth of less than about 50 feet.
 6. The methoddefined in claim 1 wherein the elevation of said ice island is at leastabout 3 feet above its maximum free-floating elevation.
 7. The methoddefined in claim 1 wherein prior to placement of said water imperviousmembrane, sea water is placed on the surface of said floating sheet ofice and frozen to form an ice body having a mass sufficiently large thatthe bottom of the ice body is just above the marine floor, and includingthe step of curing said ice under ambient conditions for a period oftime sufficient to allow brine to drain from the ice body.
 8. A methodfor constructing an artificial sea ice island in a marine body coveredby a floating sheet of ice, which comprises: placing a water imperviousmembrane on the surface of said floating sheet of ice; placing sea wateron the surface of said floating sheet of ice covered by said waterimpervious membrane to freely flood said surface to a maximum depth ofabout 2 to 6 inches under ambient conditions below the freezing point ofsaid sea water; allowing the sea water placed on said ice to freeze;repeating the alternate flooding and fReezing steps to form an ice bodyhaving a mass sufficiently large that the draft of the ice body exceedsthe depth of the marine body whereby the ice body is permanentlygrounded and the elevation of the ice body is at least about 3 feetabove its maximum free-floating elevation; establishing a plurality ofwells in the ice body above said impervious membrane spaced about 20 to50 feet apart for the drainage of brine from the ice body; and removingaccumulated brine from said wells.
 9. The method defined in claim 8wherein prior to placement of said water impervious membrane, sea wateris placed on the surface of said floating sheet of ice and frozen toform an ice body having a mass sufficiently large that the bottom of theice body is just above the marine floor, and including the step ofcuring said ice under ambient conditions for a period of time sufficientto allow brine to drain from the ice body.
 10. A method for constructingan artificial sea ice island in a marine body covered by a floatingsheet of ice, which comprises: placing sea water on the surface of saidfloating sheet of ice to freely flood the surface to a maximum depth ofabout 2 to 6 inches under ambient conditions below the freezing point ofwater; allowing the sea water placed on said ice to freeze; repeatingthe alternate flooding and freezing steps to form an ice body having amass sufficiently large that the bottom of the ice body is just abovethe marine floor; curing the ice under ambient conditions for a periodof time sufficient to allow brine to drain from the ice body; placing awater impervious membrane on the surface of the ice body; thereafterplacing additional sea water on the surface of said ice body covered bysaid impervious membrane to freely flood said surface to a depth of 2 to6 inches under ambient conditions below the freezing point of water;allowing the sea water placed on said ice to freeze; repeating thealternate flooding and freezing steps to form an ice body having a masssufficiently large that the draft of the ice body exceeds the depth ofthe marine body whereby the ice body is permanently grounded; continuingthe alternate flooding and freezing steps until the elevation of the icebody is at least about 3 feet above its maximum free-floating elevation;establishing a plurality of wells in the ice body above said imperviousmembrane spaced about 20 to 50 feet apart; and removing accumulatedbrine from said wells.